Are there any
laws on how a married couple has sex? Are there any restrictions imposed
upon the couple by Islam?

Answer:

The Holy Qur’ān has
guided the believers to observe only two restrictions while establishing
conjugal contact with their wives. Apart from them, it has not restricted
the freedom with which the wedded couple may choose to enjoy their privacy.
This is indeed a blessing of Allah that He has made them a cover for each
other under which they find solace and experience exhilaration. These
restrictions are in the following verse:

Keep away from women during their menstrual periods and do not approach them
until they are in a state of purity, then when they are clean after having a
bath, go to them from where God enjoined you. Indeed, God loves those who
constantly repent and keep themselves clean. (2:222)

Thus, the first restriction
is that copulation should be abstained from during the menstrual period of
one’s wife since it is against cleanliness and purification. The second
restriction is that carnal relationship with wife be only established
through the way Allah has prescribed. Nowhere has been mentioned such
directive as to explain the appropriate way but it is instilled in our
instincts by the Almighty. The inherent guidance, that humans are blessed
with, guides them to only have vaginal intercourse with their women.
Observance of these two restriction has been made incumbent upon all
believers. Everything else is for them to decide keeping in view their
inclinations, the objective of their inner purification and the welfare of
their offspring.